In one type of lubricating system it is conventional to provide a continuously operating lubricating pumping apparatus which feeds lubricant at a constant but controlled rate. The pressurized lubricant is metered to provide a measured flow at each lubricant outlet to the equipment to be lubricated. The measured flow may be quite different at each outlet. A pump is operated to develop sufficient pressure to feed lubricant in measured amounts to all of the equipment being serviced by the lubricator. Since, in many cases, the flow rate may be typically quite low (for example, one or two drops of lubricant per hour) the integrity of the system may be quite difficult to ascertain. One suitable method is to build up the pressure in the system to a very high level for a brief period of time and sense the pressure level and hence the integrity of the system, at critical points in the system once the test pressure is achieved.
Since the metering of the flow of lubricant is adjusted to provide lubricating fluids at a continuous rate, the pressurizing pump should preferably be tested periodically to be assured that the pump is, in fact, operating properly and that the conduits leading away from the pump are failurefree since termination of the flow of adequate lubricant due to either breaks or blockages may result in over heating and even severe damage to the equipment requiring lubricant. Although constant checking is required, the tests need not be performed more often than once every several hours, thereby requiring the use of means which is capable of developing time delays which are of the order of hours.
One technique for determining whether the system for dispensing lubricant is operating properly utilizes a pressure sensing device for sensing system pressure after each periodic build-up of liquid pressure. Such devices are employed with a timing device for generating a time interval that is of the order of several hours between successive testing operations. An indicator device is connected with the pressure sensing device to indicate an under pressure condition due to a malfunction in the system. Such prior art devices are quite expensive since they require a pressure sensing device, a complex and expensive timer and complex and expensive recycling means.
Also, it is extremely undesirable to take a pressure reading at the very initiation of the test period since the test being imposed and the test device, meter, switch, or the like, as well as the test conditions imposed, require a predetermined time to "settle" before reaching a steady state condition at which a proper reading can be taken.